1. Field of the Invention
The invention relates generally to augers which are used for conveying materials within an enclosure and particularly to augers used in moving liouid or semi-solid manure through the bed of a manure spreader.
2. Description of the Prior Art
Manure spreaders utilize various types of mechanisms, including augers, to move manure within the body of the spreader to a discharge opening. In manure spreaders which use augers to convey manure along the bed of the spreader, it is common to find that certain consistencies of manure boil up within the spreader container bed, particularly at the end of the auger, and may form bridges over the auger. Various designs have been addressed to these problems. One type of manure spreader, as shown in U.S. Pat. No. 4,467,967 to Martin, has a longitudinally positioned auger with a series of separate blades which are arranged in oppositely generated helices to urge the manure from the rear and from the front of the manure container body toward a discharge gate which is positioned in the body between the ends thereof. By moving manure from the ends to the middle portion of the body, the auger may eliminate some boil-up that would occur at an end wall, but it may not always be advantageous to have the discharge opening in the middle portion of the body. The auger shown in that patent is also raised and lowered hydraulically to break up bridging of manure within this particular spreader.
Additionally, a variety of augers and screws are currently used to move fertilizers, sludge, solid and liquid manure, and other types of materials through chutes, tubes, beds, and other containers. U.S. Pat. No. 4,206,841 to Lundgren discloses a screw conveyor which has a helical blade which extends outwardly from the shaft for conveying material along a passage from one end to the other with rotation of the screw. A plurality of helical blade segments are mounted at one end of the screw, each segment extending over an arc of about 100.degree. to about 130.degree. around the shaft of the screw. These blade segments split the main flow of material from the helix up into several smaller flows, thereby maintaining a relatively uniform flow of the conveyed material even when the conveyor is filled only to 30% of its flow capacity. The smaller blades at the end of the screw are discontinuous, that is, they are not connected to one another.
A screw-driven sludge thickener having a rotary screw extending longitudinally in an enclosure is disclosed in U.S. Pat. No. 4,528,098 to Treyssac et al. The pitch of the Treyssac screw varies in successive stages so that the distance between the flights of the screw varies in the different stages. U.S. Pat. No. 3,303,917 to Wilkes et al. discloses a material conveying and distributing device having an auger with a helical blade which varies in pitch depending upon its relative position on the shaft of the auger.
A particular problem which occurs in manure spreaders with auger feed is that with certain consistencies of manures, particularly semi-solid manure, the auger may not supply material at a continuous rate to the discharge opening, thus creating uneven and sporadic spreading of manure. Such inconsistent supply of manure may occur because the auger is rotating too slowly and does not convey manure to the discharge opening at a rate commensurate with the rate at which manure is drawn from the opening by a spreading device mounted at the opening. Conversely, inconsistent spreading can occur if the auger is rotating too fast and supplies more material to the discharge opening than can be spread by the spreading device. The excess material being fed by the auger which cannot be discharged is constrained by the sides and end panels of the manure spreading container and tends to be pushed upwardly. This action tends to compress and pack the material above the auger, resulting in a bridging condition in which the packed manure forms a solid mass which bridges over the auger. The bridged material thus cannot be fed by the auger to the discharge opening, resulting in sporadic discharge or no discharge at all.
Because the consistency of manure, particularly the semi-solid type, can vary greatly from load to load and even within a load, it is not practical to attempt to vary the auger speed to match the flow of material from the auger with the rate at which material can be spread from the discharge opening. While multi-blade augers, such as those described above, have been used in an attempt to avoid bridging and provide more continuous flow of manure, it is generally preferable that the auger have a continuous blade since continuous blades are less susceptible to damage by rocks, wood, steel or other foreign materials. Continuous blades also tend to be self-cleaning; for example, long fibrous materials, such as hay, do not hang up on the continuous flights and clog the path of flow as can happen with augers having many separate blades. Because of the self-cleaning action of a continuous flight auger, freezing of material on the auger during cold weather is also not a problem as it can be with augers having multiple blades.